1. Field of the Invention
The present invention relates to a yaw controller for actively changing vehicle yaw by operationally controlling the brake force independently developed in the right and left side wheels of the vehicle.
2. Description of Related Art
Numerous yaw controlling devices have been proposed for improving vehicle safety by automatically controlling the brake force applied to each wheel as a means of stabilizing vehicle behavior when the vehicle takes a turn. Japanese Patent Laid-Open Publication HEI 10-315943, for example, teaches a device for imparting a sufficient yawing moment to the inside of the direction of vehicle rotation by applying brake force to the rear inside wheel of vehicle yaw when vehicle drift out is detected.
Devices that automatically apply the brakes to a particular wheel to change vehicle behavior in a stabilizing direction when unstable vehicle behavior is detected when the vehicle turns are thus known.
Vehicles in which the brakes can be intentionally applied independently to right and left wheels, typically by the operator, are also known. Typical of such vehicles is the specialty vehicle such as a tractor.
A common use for actively applying the brakes independently to the right and left wheels on a tractor is to reduce the turning radius of the tractor at low speed. As taught in Japanese Patent Laid-Open Publication HEI 10-100740, separate brakes pedals are provided for the right and left wheel brakes. By separately operating these brake pedals, the operator can independently apply the brakes to the right and left wheels.
It is also desirable when driving a car, particularly when driving in car races on a race track or road rally, for the driver to be able to intentionally impart a desirable yawing moment to the vehicle in order to improve turning performance, and particularly to improve cornering performance.
Producing sufficient cornering force in each wheel is necessary in order to produce a desired yawing moment, but amount of produced cornering force varies greatly with the driving conditions of the vehicle.
For example, when the steering wheel is turned a large steering angle while driving at high speed, the cornering force of the front wheels becomes saturated and understeering occurs. The vehicle thus drifts out. Furthermore, when the front wheels slip on a road surface with a low coefficient of friction (xcexc), substantially no cornering force is produced, understeering results, drift out occurs again, and the desired yawing moment cannot be produced.
By automatically applying brake force to the rear inside wheel of the yaw when drift out is detected, the yaw control device taught in Japanese Patent Laid-Open Publication HEI 10-315943 can limit drift out from continuing when it occurs.
This yaw control device only works to change vehicle behavior in a stabilizing direction, however, and therefore cannot be used by the driver to achieve a desired turning performance in order to limit drift out before it is detected or to improve cornering performance with a slight oversteer.
It should be noted that the tractor braking system that allows the operator to independently apply the brake force to the right and left wheels is designed for making small radius turns at low speed. It is not designed to apply specific brake force to the wheels in order to achieve a desired yaw moment. A driver therefore cannot use this braking system to achieve a desired turning performance.
Even if such a system could be used to actively selectively apply brake force to the right and left wheels at medium or high speeds, the brake pedals must be separately operated with a tractor-like brake system. Combined with the need to operate other pedals (such as the accelerator and clutch) is considered, operation becomes extremely complex. Furthermore, it is extremely difficult to independently operate right and left brake pedals with the degree of fine control required to achieve a particular yaw moment, and it is, therefore, not practically possible to achieved a desired yaw moment.
The present invention was conceived with the above described problems in mind, and the intent of the invention is to provide a vehicle yaw controlling apparatus that enables a driver to achieve a desired turning performance, and particularly a desired cornering performance, by actively applying brake force independently to the right and left wheels through a simple operation.
To achieve the above object, a yaw controlling apparatus according to the present invention is a vehicle brake system capable of independently controlling right and left wheels, and has a pair of right and left operating switches disposed so that the driver can easily and independently operate the right and left operating switches while holding the steering wheel with both hands; and a control device for applying brake force to the brake unit of one of the right and left wheels when the driver operates one of the operating switches, and applies brake force to the brake unit of the other of the right and left wheels when the driver operates the other operating switch.
The brake switches can be therefore be operated separately from the foot-operated brake pedal at a position easily accessible to the hands. The operation used to independently apply brake force to the right and left wheels is thus uncomplicated and differential brake force can be easily controlled by the driver. Operability and safety can thus both be improved.
In this vehicle yaw controlling apparatus, the left operating switch preferably controls a left wheel brake unit, and the right operating switch controls a right wheel brake unit. The braking effect intended by the driver can thus be easily achieved while operability is improved and intuitive.
Further preferably, the brake force developed in a brake unit changes according to the applied pressure or stroke of the operating switch that was operated. Brake force accurately reflecting the brake force desired by the driver can therefore be developed in the particular brake unit. Operation can thus be desirably optimized, and handling stability improved.
Yet further preferably, the vehicle yaw controlling apparatus additionally has a control prohibiting means for prohibiting operation by the control device under one or more specific conditions. Driving safety and steering stability can thus be assured because operation of the yaw controller can be prohibited when, for example, the braking effect requested by the driver is inappropriate to vehicle behavior.
In one particular aspect of the invention, this control prohibiting means is a driver identification means for permitting use of the yaw controlling apparatus only by a particular driver. Driving safety and steering stability can thus be assured because unknown drivers with potentially low level driving skills, for example, are not allowed to use the yaw controlling apparatus.
Yet further preferably in this case the control device has a manual mode for developing brake force in a brake unit as directed by the driver, and an automatic mode for automatically correcting the brake force indicated by the driver operation of the operating switch according to specific conditions and then developing the corrected brake force in the brake unit. It is therefore possible to assure that the control is mode appropriate to how the vehicle is to be driven. As a result, both of a control state in accordance with a driving scenario of the vehicle and a control state in accordance with the driver""s intention can be obtained.
Yet further preferably in this case the vehicle yaw controlling apparatus has a mode selecting unit enabling the driver to s elect either the manual mode or the automatic mode. In this case the driver can select the appropriate control mode appropriate to how the vehicle is to be driven. As a result, both of a control state in accordance with a driving scenario of the vehicle and a control state in accordance with the driver""s intention can be obtained.
Yet further preferably, the brake force developed in a brake unit is determined so that the sensitivity of the operating switch is greater when initially operated and gradually declines as switch operation continues. By thus limiting the change in brake force in the high brake force range to gradual change, the wheel brakes can be prevented from locking up and steerability can be assured.
Yet further preferably, the brake force developed in a brake unit is determined so that the increase in brake force in response to operating switch operation decreases as vehicle speed increases. The change in brake force at high vehicle speeds can thus be kept small, improving steerability and safety at high speed.
In a preferred aspect of the invention, the control prohibiting means of the vehicle yaw controlling apparatus prohibits yaw moment control when the vehicle yawing direction is detected to be opposite the steering direction. Yaw moment control is thus prohibited when a counter steering condition is detected.
If the operating switch on the same side as the direction in which the steering wheel is turned is operated as usual during a counter steering condition, that is, when the steering wheel is turned opposite the yawing direction of the vehicle, the effectiveness of counter steering will be diminished and the tendency of the vehicle to spin enhanced. By disabling yawing moment control when counter steering is detected, loss of steering stability resulting from misoperation can be reliably prevented.
Further preferably, the control prohibiting means prohibits yaw moment control when the steering angle exceeds a specific large angle, and thus prohibits yaw moment control when the steering wheel is turned greatly. Steering stability is thus assured when the steering wheel is turned to an angle effecting a quick change in vehicle direction, and vehicle instability resulting from the steering angle exceeding the tire limits can be prevented.
Yet further preferably, the control prohibiting means prohibits yaw moment control when engine output exceeds a specific high output level. Yawing moment control is thus prevented and steering stability is assured when transfer of high engine output to tires on one side could easily make vehicle behavior unstable.
Yet further preferably, the control prohibiting means prohibits yaw moment control when braking as a result of the driver operating the brake pedal is detected. In this case yawing moment control is prevented from interfering with normal brake operation, and thus assures reliable braking as expected by the driver.
With a vehicle yaw controlling apparatus according to a further aspect of the invention, brake force is developed only in the brake unit of the rear wheel on the side corresponding to the operating switch. In this case yawing moment control is prevented from interfering with vehicle behavior resulting from front wheel steering, and steerability is thus improved.
Yet further preferably, the vehicle yaw controlling apparatus also has a yaw rate brake force regulating means for regulating the brake force developed in a brake unit so that the actual yaw rate developed in the vehicle by the control device does not exceed an appropriate yaw rate range. Safety is thus improved by automatically suppressing excessive yawing moment adjustment by the driver.
Yet further preferably, the vehicle yaw controlling apparatus has a slipping brake force regulating means for regulating the brake force developed in a brake unit so that the wheel slip rate is controlled to less than or equal to a specific slip rate. Safety is assured in this case by controlling the developed brake force within an acceptable wheel slip range.
When the vehicle is equipped with a slip control device (for example, an antilock brake system) for suppressing wheel slipping, or a dynamic stability control system for stabilizing vehicle behavior when cornering, the yaw controlling apparatus further preferably has a means for prioritizing control intervention when control by the slip control device or dynamic stability control system starts to operate. Safety can be improved in this case because a change in vehicle behavior from misoperation or excessive operation by the driver is reliably prevented.
The operating switches of our vehicle yaw controlling apparatus can be either push devices disposed on the front of the steering wheel, or pull devices disposed on the back of the steering wheel.
When the operating switches are push devices on the front of the steering wheel, they can be easily operated while glancing at the switches without taking either hand off the steering wheel, and can be operated with an extremely simple pushing operation. Switch operability is thus excellent.
Furthermore, when the operating switches are pull devices on the back of the steering wheel, the hands will not interfere with the operating switches when using the steering wheel because the switches are not on the front of the steering wheel, and unintentional operation of the switches can be reliably prevented.
Yet further preferably, the vehicle yaw controlling apparatus evaluates vehicle behavior to automatically correct the ratio of brake force distributed to the front and rear wheels on the side corresponding to the operated operating switch. The distribution of brake force to the front and rear wheels on the side of the operated switch is thus optimally controlled to achieve optimum vehicle behavior.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.